This invention relates to a telephone apparatus equipped on vehicles, and more particularly to a road-vehicle telephone apparatus which is dialed using dial keys provided on a steering operation board in the vicinity of a steering wheel.
In vehicles, since a steering wheel is positioned nearest to the driver, particularly to his hand, an operation board equipped with a variety of keys, switches or the like adapted to control and command road-vehicle apparatus and units is preferably mounted at the central portion of the steering wheel for the purpose of improving operability.
However, a steering mechanism adapted to transmit a rotational movement of the wheel to a steering shaft is complicated, so that it is difficult to wire signal cables for connecting the operation board mounted at the center of the steering wheel (i.e., steering operation board) to a stationary control unit. To facilitate such wiring work, pipes for wiring and/or slip rings for connection must be additionally mounted to the steering mechanism and arranged in a manner without intervening operation thereof. Further, since the mounting space allocated to the steering mechanism is limited, such wiring work will be quite difficult.
In view of the above, the applicant of this patent application has previously proposed an improved system (U.S. patent application Ser. No. 399,582 filed on July 19, 1982) wherein the operation board is connected to the stationary control unit using slip rings and brushes, thereby to transmit electric power and signals through such connection lines. With this, it is possible to supply the operation board with source power and to transmit much information generated therefrom without the need to use numerous lines.
In case a telephone apparatus is equipped on the vehicle, a telephone set is usually placed at the center between the driver's seat and the passenger seat in order that the persons sitting in the passenger seat or the rear seats can also use the telephone set. But when the driver attempts to operate a dial of the telephone set, he must have a receiver by one hand and operate the dial by the other hand, so that he is practically unable to dial a call while driving the vehicle. Therefore, the applicant of this patent application has previously proposed a dial signal transmission system for a steering operation board (U.S. patent application Ser. No. 440,660 filed on Nov. 10, 1982) wherein dial keys are provided on the steering operation board in the vicinity of the steering wheel to make it easy for the driver to dial a number. Even with such an improved system, however, the driver has to operate the dial keys by touch during driving of the vehicle and hence the dial keys are liable to be operated by mistake. Since such erroneous operation of the dial keys may trouble the called subscriber, it is preferred to dial a number only when the vehicle is stopped.